Many individuals with multiple sclerosis, cerebral palsy, spinal cord injuries, and other degenerative conditions, are locked into a private world of silence and suffering. These individuals cannot effectively communicate with their environment due to the impairment of the neuronal pathways in the brain and spinal cord that control their bodily movements. For these individuals, life is very bleak indeed.
In the absence of a medical treatment to restore the damaged nervous system, three options exist for restoring function. A first option is to augment the capabilities of the remaining pathways. Muscles that remain under voluntary control can be substituted for paralyzed muscles. This substitution, however, is often awkward and limited. Some individuals with massive brainstem lesions can use eye movements to answer questions or even operate a word processing program. Severely dysarthric individuals have been taught to use hand movements to produce synthetic speech.
A second option is to detour around the points of damage. People with spinal cord transection can use the electromyographic activity (EMG) from muscles above the level of the lesion to control direct electrical stimulation of paralyzed muscles, and thereby produce useful movement. This technique has restored significant hand and forearm function to people with cervical cord lesions, and also may permit individuals with thoracic cord lesions to walk again.
A third option is to provide the brain with new channels by which control and communication can be established. This third option featuring new channels of communication is one that has not received a great amount of attention. There is art, however, that suggests that electroencephalographic (EEG) activity can provide new channels for communicating.
The EEG reflects activity in the underlying brain. Thus, in theory, the intentions of the individual might be detected in the EEG. Unfortunately, this is not easily accomplished in practice. The resolution and reliability of the information detectable in the spontaneous EEG is severely limited by the vast number of electrically active neuronal elements; the complexity of the brain and head geometry; and the variability of brain operations.
In the sixty-six years since the first description of scalp-recorded EEG, many investigators have attempted to demonstrate human abilities to control a variety of EEG phenomena and use them for therapeutic purposes. The literature reports successful conditioning of the visual alpha rhythm, slow potentials, and the mu rhythm. For example, research has sought to increase specific EEG components and thereby reduce seizure frequency.
Few investigators have studied rapid bidirectional control, i.e., the ability to increase and decrease a component rapidly, which is essential for communication. Most important, no one has demonstrated such control in more than one dimension simultaneously. For example, no one has developed a method that uses the EEG to control both vertical and horizontal positions on a visual display simultaneously.
The alpha band is a frequency band of from 8 to 12 Hz in the scalp recorded EEG. The most prominent component of this band is the visual alpha rhythm. It is maximum over the occipital (i.e., visual) cortex in awake individuals with eyes closed. Eye opening will reduce, desynchronize, or block this rhythm.
Another component of the alpha band is the mu rhythm, which is 8 to 12 Hz activity over sensorimotor cortex. The mu rhythm is also known in the literature as "wicket", "comb", or "arceau" rhythm. The mu rhythm is most prominent in awake, relaxed individuals whose eyes are open. It is usually reduced or desynchronized by contralateral movements. It is believed to be an idling rhythm of the sensorimotor cortex, in contrast to the visual alpha rhythm, which is an idling rhythm of the visual cortex. It is probably the analog of the 12 to 16 Hz sensorimotor rhythm found in cats.
Only recently has the mu rhythm been shown to be present in most individuals. The recent studies have also shown the mu rhythm to contain a number of different components. The different components all share the same frequency band, posterior frontal/anterior parietal location, and attenuation with movement. However, these components differ in exact frequency, precise localization, and/or exact relation to movement. It is these differences that have led scientists to define them as different components. For example, one mu rhythm component might have a frequency of 11 Hz, be sharply focused over sensorimotor cortex on one side, and decrease appreciably before movement, while another mu rhythm component might have a frequency of 9 Hz, be diffusely localized over the midline, and decrease somewhat later. The new findings suggest that mu rhythms are ubiquitous and complex. It has also been demonstrated that individuals can increase mu rhythm amplitudes with the proper conditioning. This control is separate from the rhythm's normal responsiveness to contralateral movement.
The present invention teaches that mu rhythms can be used as a new EEG-based, brain-computer interface.
The current invention has provided a means by which humans can precisely and quickly increase and decrease rhythm components. Furthermore, this rapid bidirectional (i.e., increase/decrease) control can be achieved over more than one component at the same time. That is, it can be multidimensional. The result is that one component can be used to control horizontal movement while another is being used to control vertical movement. Such an interface could be of great value to those severely impaired individuals suffering from motor impairments due to brainstem stroke, cervical spinal cord injury, severe cerebral palsy, amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease), etc.
The most severely impaired individuals are presently confined in their communications to very limited systems comprising eye blinks, eye movements, or breathing changes. Even these limited movements may be impaired so that some individuals are without communication. They are literally "locked in" their bodies.
The present inventors recognize that, in order to provide such severely incapacitated individuals with a means of communicating with the outside world, it is necessary to provide them with a means that is equivalent to that of working a computer mouse or joystick.
The current invention also contemplates that the use of multidimensional EEG-based communication can be a more effective communication tool for less severely impaired individuals, whose movements, while adequate to provide communication, are difficult or tiring.